Conventionally, there have been operational amplifiers, in each of which a detection circuit is connected to a current source in parallel and the current source supply is increased only when there is an input level difference detected at the detection circuit. (For such operational amplifiers, refer to JP-A-Hei 11-1360441, JP-A-2004-128815, and JP-A-Hei 11-88076.)
Furthermore, there have also been other type operational amplifiers, in each of which the current source increases the current supply when there is an input level difference in a voltage follower, that is, when there is a level difference between an input and an output (refer to JP-A-2006-157607 and JP-A-2000-349570).